Ultraviolet rays reaching the Earth's surface from the sun can be classified into long wave ultraviolet rays UVA (from 320 to 400 nm) and medium wave ultraviolet rays UVB (from 280 to 320 nm). UVA can be classified further into UVAII (from 320 to 340 nm) and UVAI (from 340 to 400 nm). Even brief exposure to UVB causes sunburn, inflammation of the skin such as erythema and edema and several days later, it leads to pigmentation. Thus, UVB has a tanning action. Moreover, UVB is said to induce skin aging and cancer. Exposure to UVA, on the other hand, changes a pale-color melanin pigment existing in the epidermis into a dark-color melanin pigment and thereby darkens the skin, which phenomenon is called “immediate pigment darkening”. In addition, UVA is said to reduce resilience or elasticity of the skin.
Sunscreen cosmetic compositions containing an organic ultraviolet absorber capable of efficiently absorbing ultraviolet light or ultraviolet protection powders capable of scattering ultraviolet light have been employed in order to protect the skin from ultraviolet light. Many sunscreen cosmetic compositions which have recently been put on the market are W/O types having long lasting ultraviolet protection effects and is easily applicable to the skin. Their ultraviolet protection effects are obtained by incorporating, in an outer oil phase of such emulsions, an organic ultraviolet absorber or ultraviolet protection powders (hydrophobic ultraviolet protection powders) having a surface subjected to hydrophobic treatment in combination.
In these emulsions, however, an ultraviolet protection agent is present only in one phase (oil phase) so that the ultraviolet protection agent cannot be applied to the skin uniformly. As a result, the agent often fails to fully produce its effects.
Various investigations have been made with a view to attaining more uniform distribution of an ultraviolet protection agent on the skin when an emulsion composition containing it is applied to the skin. For example, it is described in Patent Document 1 that use of water-dispersible ultrafine titanium dioxide and oil-dispersible ultrafine titanium dioxide in combination enables more uniform distribution of the ultraviolet protection agents on the skin, thereby synergistically improving protection from ultraviolet light.
In Patent Document 2, it is described that the combined use of an oil soluble ultraviolet absorber and a water soluble ultraviolet absorber enables improvement of ultraviolet protection effects.
These compositions however have insufficient resistance to sweat or water because of the water soluble ultraviolet protection agent contained therein and they are not satisfactory in the maintenance of ultraviolet protection effects.    [Patent Document 1] JP-A-6-16527    [Patent Document 2] JP-A-8-506574